Lens assembly and optical imaging using same

ABSTRACT

A lens assembly includes, in order from an object side to an image side: a first lens; a first meniscus lens in optical communication with the first lens; a second meniscus lens in optical communication with the first meniscus lens; an aperture stop in optical communication with the second meniscus lens; a fourth lens in optical communication with the aperture stop; and a bi-convex lens in optical communication with the fourth lens. The lens assembly is a four group, five element, lens assembly that is constructed so that at least one of the lenses may be replaced without also requiring the other lenses in the assembly to be significantly changed, resulting in a “flexible” construction. The lens assembly may be adapted to provide a field of view of approximately 15 degrees; approximately 0% vignetting within the field of view; and a distortion of the image of less than approximately 1%. Multiple lens assemblies and detectors may be provided in a single housing.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/798,841, and claims the benefit under 35 U.S.C. § 120 of U.S.application Ser. No. 10/798,841, entitled “LENS ASSEMBLY AND OPTICALIMAGING SYSTEM USING SAME,” filed on Mar. 11, 2004, which is hereinincorporated by reference in its entirety.

BACKGROUND OF INVENTION

1. Field of Invention

The present application relates to lens assemblies for use in opticalimaging systems.

2. Discussion of Related Art

Lens assemblies for imaging objects are known. When designing lensassemblies, a designer may take into account one or more desiredcharacteristics or constraints, such as focal length, back focal length,environment, spacing of lenses, aperture size, overall assembly length,field of view, cost and/or ease of manufacture, ease of use, or anyother characteristics or design constraints.

However, it is often difficult to design a lens assembly that meetsthese sometimes competing design constraints, and this difficulty may becompounded when the lens assembly is intended to be used with additionalcomponents, or in specific applications. Examples of such additionalcomponents may be filters, lens covers, aperture stops, electronicdetectors, electronic devices, or any other components. The resultingimage quality produced by the lens assembly is often necessarilycompromised in order to satisfy these many design constraints, or inorder to achieve certain desired optical characteristics.

SUMMARY OF INVENTION

In one aspect, a lens assembly is provided. The lens assembly includes,in order from an object side to an image side: a first lens; a firstmeniscus lens in optical communication with the first lens; a secondmeniscus lens in optical communication with the first meniscus lens; anaperture stop in optical communication with the second meniscus lens; afourth lens in optical communication with the aperture stop; and abi-convex lens in optical communication with the fourth lens.

In another aspect, a lens assembly is provided and includes a pluralityof lenses for producing an image of an object. The plurality of lensesis adapted to provide: a field of view of approximately 15 degrees;approximately 0% vignetting within the field of view; and a distortionof the image of less than approximately 1%.

In yet another aspect, an imaging device for imaging an object isprovided. The imaging device includes an imaging device housing and aplurality of individual lens assemblies disposed at least partiallywithin the imaging device housing. A plurality of detectors is disposedat least partially within the imaging device housing. Each detector isoptically arranged relative to a respective one of the lens assembliesto receive images from the respective lens assembly.

In yet another aspect, a lens assembly is provided. The lens assemblyincludes a first lens arrangement comprising at least one lens elementhaving at least one initial parameter; and a second lens arrangement inoptical communication with the first lens arrangement. The second lensarrangement comprises at least one lens element having at least oneinitial parameter. The first and second lens arrangements cooperate toproduce an image having an image characteristic within a range ofacceptable image characteristics. A first parameter of the at least oneinitial parameter of the first lens arrangement may be changed whilemaintaining one or more parameters of the at least one initial parameterof the second lens arrangement within a desired range so that the imagecharacteristic is maintained within the range of acceptable imagecharacteristics.

According to yet another aspect of the invention, a lens system isprovided. The lens system comprises a plurality of lens elements, and anaperture stop, each lens element having a lens surface defined by aradius of curvature (r), a thickness (d), an index of refraction (n),and a dispersion (v), the plurality of lens elements being spaced fromeach other by a distance (d). The lens system satisfies at least one ofthe following conditions:

-   -   a) 0.98*f<d₁+d₂+d₃+d₄+d₅+d₆+d₇+d₈+d₉+d₁₀+d₁₁+d₁₂+d₁₃+d₁₄<1.02*f;        or    -   b) 0.47*f<d₁+d₂+d₃+d₄+d₅+d₆+d₇+d₈+d₉<0.61*f; or    -   c) 20.4 mm<f₁<30.5 mm when assembly scaled to f=25 mm; or    -   d) −100 mm<f_(2,3)<15 mm when assembly scaled to f=25 mm; or    -   e) 1.49<n₁<1.52 and v₁≧70; or    -   f) 1.8<n₂ and 24<v₂<26; or    -   g) −50 mm<f₄<−35 mm when 1.5<n₄<1.72 and when assembly scaled to        f=25 mm; or    -   h) 110 mm<f₅<540 mm when n₅>1.7 and when assembly scaled to f=25        mm; or    -   i) r₇/r₁₀<0.3 when n₄/n₅>0.98; or    -   j) r₇/r₁₀>0.5 when n₄/n₅<0.90;    -   where:    -   f represents an effective focal length of the plurality of        lenses; f₁ represents a focal length of a first lens element; f₄        represents a focal length of a fourth lens element; f₅        represents a focal length of a fifth lens element; f_(2,3)        represents a focal length of a combination of a second lens        element and a third lens element; d₁ represents a thickness of        the first lens element; d₂ represents a gap distance from an        image side surface of the first lens element to an object side        surface of the second lens element; d₃ represents a thickness of        the second lens element; d₄ represents a thickness of the third        lens element; d₅ represents a gap distance from an image side        surface of the third lens element to the aperture stop; d₆        represents a gap distance from the aperture stop to an object        side surface of the fourth lens element; d₇ represents a        thickness of the fourth lens element; d₈ represents a gap        distance from an image side surface of the fourth lens element        to an object side surface of the fifth lens element; dg        represents a thickness of the fifth lens element;        d₁₀+d₁₁+d₁₂+d₁₃+d₁₄ represents a gap distance from an image side        surface of the fifth lens element to an image plane; n₁        represents an index of refraction of the first lens element; n₂        represents an index of refraction of the second lens element; n₄        represents an index of refraction of the fourth lens element; n₅        represents an index of refraction of the fifth lens element; v₁        represents a dispersion of the first lens element; v₂ represents        a dispersion of the second lens element; v₄ represents a        dispersion of the fourth lens element; v₅ represents a        dispersion of the fifth lens element; r₇ represents a radius of        curvature of the object side surface of the fourth lens element;        and r₁₀ represents a radius of curvature of the image side        surface of the fifth lens element.

Various embodiments of the present invention provide certain advantages.Not all embodiments of the invention share the same advantages and thosethat do may not share them under all circumstances.

Further features and advantages of the present invention, as well as thestructure of various embodiments of the present invention are describedin detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 shows an example of a structure of a lens assembly according toan embodiment of the present invention.

FIGS. 2-5 illustrate lenses of a lens assembly according to the presentinvention.

FIG. 6 illustrates an example of a housing for holding lenses of a lensassembly according to the present invention.

FIG. 7 illustrates the housing of FIG. 6 with lenses of a lens assemblyaccording to the present invention.

FIGS. 8A and 8B illustrate a lens retainer for use in connection withthe housing of FIG. 6.

FIG. 9 illustrates an example of a housing for holding lenses of a lensassembly according to the present invention.

FIG. 10 illustrates the housing of FIG. 9 with lenses of a lens assemblyaccording to the present invention.

FIGS. 11A and 11B illustrate a lens retainer for use in connection withthe housing of FIG. 9.

FIG. 12 shows an example of a structure of a lens assembly according toan embodiment of the present invention.

FIG. 13 shows an example of a structure of a lens assembly according toan embodiment of the present invention.

FIG. 14 shows an example of a structure of a lens assembly according toan embodiment of the present invention.

FIG. 15 is an illustrative embodiment of values of aberrationsassociated with a lens assembly according to an aspect of the presentinvention.

FIG. 16 is a schematic representation of a multi-head imaging deviceaccording to an aspect of the present invention.

FIG. 17 is a perspective view of an imaging device including themulti-head imaging device.

DETAILED DESCRIPTION

According to aspects of the invention, the lens assembly is constructedto accommodate certain, often competing, design characteristics. In oneaspect, the lens assembly provides high optical performance in an easyto manufacture system (e.g., construct, assemble, and align). The lensassembly is also suitable for use in connection with additionalcomponents, such as filters and/or electronic detectors, such as CCD'sand/or CMOS's.

According to an aspect of the invention, the lens assembly provides afield of view of approximately 15 degrees, with approximately 0%vignetting within the indicated field of view, and with less thanapproximately 1% distortion of an image. The approximately 15 degreefield of view may range from 14.5 degrees to 15.5 degrees. In oneembodiment, the lens assembly provides these performance characteristicsin conjunction with a high speed aperture, for example, approximatelyf4. The lens assembly may be a moderate telephoto lens assembly, whereinit may be constructed to provide a ratio of the length of the lensassembly to the focal length of approximately 1.0.

According to another aspect of the invention, the lens assembly includesan aperture stop, with the lens assembly being non-symmetrical about theaperture stop. According to one embodiment, the non-symmetrical lensassembly includes four lens groups and five lens elements. The secondand third lens elements, constituting the second lens group, have highlysensitive design parameters in comparison to the design parameters ofthe first, fourth, and fifth lens elements. Thus, the second and thirdlens elements have tighter manufacturing tolerances as compared to theother lens elements. The aperture stop may be disposed between the thirdand fourth lenses.

In one embodiment, the second lens group includes second and third lenselements, cemented together. The second and third lens elementsconsistently take the form of meniscus lenses. The fourth lens groupincludes a fifth lens element. The fifth lens element consistently takesthe form of a bi-convex lens element. The fifth lens element may haveapproximately equal but opposite radii of curvature for a surfaceproximate the object side of the lens assembly and a surface distal theobject side of the lens assembly, respectively, which may be termed inthe art as a “perfect” lens element. The first lens group includes afirst lens element, that may be either a meniscus lens element having aconvex surface proximate the object side of the lens assembly, and aconcave surface distal the object side of the lens assembly, or aplano-convex lens, having a convex surface proximate the object side ofthe lens assembly and a planar surface distal the object side of thelens assembly. The third lens group includes a fourth lens element, thatmay be either a meniscus lens element having a concave surface proximatethe object side and a convex surface distal the object side, or abi-concave lens, having concave surfaces proximate and distal the objectside of the lens assembly. In one embodiment, the above-listed lenselements are immediately adjacent each other. In one embodiment, anaperture stop (also referred to as aperture plate, aperture, stop, ormicro-plate) is disposed between the second and third lens groups, andin one embodiment, between the third and fourth lens elements. Inanother embodiment, the aperture stop is disposed between the third andfourth lens elements, with the other lens elements being immediatelyadjacent each other.

The lens assembly may also incorporate filter plates, while maintaininga high quality image. The filter plates may be low-pass filter plates,color correction plates, or any other type of filter plate. In oneembodiment, one or more parallel filter plates having planar surfacesmay be disposed between the fifth lens element and the image plane. Suchfilter plates often produce aberrations, such as coma and astigmatism,or other aberrations, in the resulting image of the object. An aspect ofthe present invention provides correction for such coma and astigmatism,or other aberrations, introduced by using plane parallel plates with alens assembly. According to one embodiment, the lens assembly containscompensating aberrations to compensate the aberrations of plane parallelplates.

According to another aspect of the invention, a multi-head imagingdevice is provided. The multi-head imaging device includes two distinctlens assemblies that may be identical to each other or different fromeach other. The multi-head imaging device may further comprise twodistinct CCD detectors, or other types of detectors (e.g., CMOSdetectors), or imaging media, or any suitable combination of detectorsor imaging media. The two distinct lens assemblies may each beassociated with at least one of the two distinct detectors and/orimaging media.

According to one embodiment, a user may view an image provided by one ofthe two distinct lens assemblies. The user may choose which lensassembly through which to view an object and may switch lens assembliesthrough which to view the object, as desired. Thus, a user may manuallyswitch between lens assemblies. Alternatively or in addition, switchingbetween views may occur automatically and may be programmed orcontrolled by software. In one embodiment, switching between lensassemblies may occur in response to an event (which may be a programmedevent or a detected event). In one embodiment, switching between lensassemblies may occur upon motion occurring in the field of view or apredetermined object in or entering the field of view. In oneembodiment, switching between views may occur instantaneously.

Although certain embodiments are described as including only two lensassemblies, the present invention is not limited in this respect, asadditional lens assemblies may be provided in a multi-lens assemblyhead.

According to one embodiment, a first lens assembly in the multi-lensassembly head is a constant focus lens assembly. A second lens assemblyis a wide-angle lens assembly. According to one embodiment, the imageproduced by the wide-angle lens assembly is generally viewed, and theimage produced by the constant focus lens assembly is used to provide amagnified view of a point or object of interest in the field of view ofthe wide-angle lens assembly. Of course, the opposite may hold, as thepresent invention is not limited in this respect. For example, a viewermay first view an object through a relatively higher-magnification lensand then switch to a wider field of view lens.

According to another aspect of the invention, the lens assembly is of aminiature and compact design, which may find suitable use as a securitycamera, an inspection camera, or as a personal use camera, as will bediscussed in more detail below.

The above aspects of the invention may be employed singularly or in anysuitable combination as the present invention is not limited in thisrespect. Also, any or all of the above aspects may be employed in arelatively small imaging system; however, the present invention is notlimited in this respect, as aspects of the invention may be used on anytype of imaging system, including those that may be larger or smallerthan the embodiments described. In addition, the lens assembly may beemployed in any device and may be employed with any type of camera,including digital or film-based cameras. Various aspects and embodimentsof the invention will now be described in more detail with respect tothe accompanying figures. The invention is not, however, limited to theaspects and embodiments shown. In some of the figures that follow,specific numerical values are used to describe the elements and/oroptical parameters. It should be appreciated that such values are notnecessarily limiting, but rather, that the values may fall within arange of acceptable limits.

In the following description, radii of curvature are listed for severalsurfaces of lens elements. As is conventional, the radii will be listedwith a positive value when the surface bows toward an object side of thelens, and with a negative value when the surface bows toward an imageside of the lens. The specific numbers that follow relate to lensassemblies designed with a specific focal length. It should beappreciated that the values will differ if the lens assemblies arescaled to a different focal length. Such scaling of components is meantto be encompassed within the present invention.

FIG. 1 shows one embodiment of a lens assembly according to the presentinvention. The lens assembly 100 comprises five lenses, L₁-L₅, anaperture stop 106 and two planar plates, F₁ and F₂, all disposed betweenan object side 120 and an image plane 122. As illustrated, and discussedbelow in more detail, lenses L₁-L₃ in this embodiment are meniscuslenses having positive radii of curvature. Lens L₄ is a meniscus lenshaving negative radii of curvature. Lens L₅ is a bi-convex lens.

The aperture stop 106, having a surface S₆, is disposed between lens L₃and lens L₄. In this embodiment, the aperture stop is a fixed aperturestop, and may have a high speed, for example, f4. Other aperture stopf-numbers may be used, as the present invention is not limited in thisrespect. Further, although in this embodiment, the aperture stop isfixed, the present invention is not limited in this respect, as variableor changeable (i.e., replaceable) aperture stops may be employed.

Planar plates F₁ and F₂ may be any planar plates, as is known to thoseof skill in the art, and the invention is not limited in this respect.For example, planar plate F₁ may be a filter plate, such as a low-passfilter plate, or any other type of filter plate. Planar plate F₂ may becover glass, used to cover a detector located at the image plane 122.

The introduction of planar parallel plates, such as F₁ and F₂ in FIG. 1,into an optical system may introduce aberrations into the system.However, such planar plates may be necessary for use with CCD or CMOSdevices. A lens assembly which is designed in the absence of planarplates may suffer performance degradation if one or more planar platesare subsequently inserted into the assembly. It may be necessary todesign the lens assembly to compensate for such aberrations, in order toensure that a satisfactory image quality may result with the use of theplanar plates. Thus, according to one aspect of the invention, as willbe described in more detail below, the combination of lenses L₁-L₅compensates for any aberrations introduced by the planar parallel platesF₁ and F₂.

The lenses of the lens assembly 100 according to the present embodimentare now described in more detail in connection with FIGS. 2-6. Thespecific values listed in connection with FIGS. 2-6 pertain to the lensassembly 100 when scaled for use with a 1/2 inch CCD detector located atthe image plane 122. The focal length, f, of a lens assembly scaled foruse with a 1/2 inch CCD detector is approximately 29.9 mm. The specificvalues listed in connection with FIGS. 2-6 may change if the lensassembly 100 were scaled for use with a different device and/ordetector, as would be known to one of skill in the art. Such scaling ismeant to be encompassed by the present invention.

As shown in FIG. 2, lens L₁ has a surface S₁ proximate the object side120 and a surface S₂ distal the object side. In this embodiment, surfaceS₁ has a radius of curvature of approximately 12.6 mm, while surface S₂has a radius of curvature of approximately 72.95 mm. Surfaces S₁ and S₂are both coated with approximately 0.5876 μm of anti-reflective coating(hereinafter Ar, or AR), as would be known to one of skill in the art,although other suitable coatings (or no coating at all) may be employed,as the present invention is not limited in this respect. The thickness,d₁, of lens L₁ is approximately 1.83 mm. Lens L₁ also has a circulardiameter D₁ of approximately 10 mm. The index of refraction, n₁, isapproximately 1.487, while the dispersion, v₁, is approximately 84.47.Lens L₁ is a crown glass. It should be appreciated that the presentinvention is not limited in this respect, as other suitable materialsand/or other suitable indices of refraction and/or dispersion may beemployed.

FIG. 3 illustrates lenses L₂ and L₃ of FIG. 1. Surface S₃ of lens L₂ isproximate the object side 120 and has a radius of curvature ofapproximately 8.45 mm. Lenses L₂ and L₃ share a common surface S₄, whichin this embodiment has a radius of curvature of approximately 5 mm. Thethickness d₃ of lens L₂ is approximately 2.33 mm. Lens L₂ is circularwith a diameter D₂ of approximately 8.5 mm. Lens L₂ has an index ofrefraction, n₂, of approximately 1.805 and a dispersion, v₂, ofapproximately 25.43. Lens L₂ is a flint glass. It should be appreciatedthat the present invention is not limited in this respect, as othersuitable materials and/or other suitable indices of refraction and/ordispersion may be employed.

Lens L₃ has a surface S₅ with a radius of curvature of approximately 5.9mm, such that the thickness d₄ of lens L₃ is approximately 3.08 mm. LensL₃ also has a circular diameter D₃ of approximately 8.5 mm. Lens L₃ hasan index of refraction, n₃, of approximately 1.620 and a dispersion, v₃,of approximately 60.32. Lens L₃ is a crown glass. It should beappreciated that the present invention is not limited in this respect,as other suitable materials and/or other suitable indices of refractionand/or dispersion may be employed.

Surface S₃ of lens L₂, and surface S₅ of lens L₃ are coated withapproximately 0.5876 μm of Ar, although other suitable coatings (or nocoating at all) may be employed, as the present invention is not limitedin this respect. It is also seen in FIG. 3 that lenses L₂ and L₃ arecemented together. This may be accomplished by any suitable means, forexample, UV epoxy.

FIG. 4 illustrates lens L₄ of lens assembly 100. Lens L₄ has a surfaceS₇ proximate the object side 120 and a surface S₈ distal the objectside. In this embodiment, surface S₇ has a radius of curvature ofapproximately −6.9 mm, while surface S₈ has a radius of curvature ofapproximately −8.55 mm. Surfaces S₇ and S₈ are both coated withapproximately 0.5876 μm of Ar, although other suitable coatings (or nocoating at all) may be employed, as the present invention is not limitedin this respect. The thickness, d₇, of lens L₄ is approximately 1.24 mm.Lens L₄ also has a circular diameter D₄ of approximately 6 mm. Lens L₄has an index of refraction, n₄, of approximately 1.717, while thedispersion, v₄, is approximately 47.96. Lens L₄ is a crown glass. Itshould be appreciated that the present invention is not limited in thisrespect, as other suitable materials and/or other suitable indices ofrefraction and/or dispersion may be employed.

FIG. 5 illustrates lens L₅ of lens assembly 100. Lens L₅ has a surfaceS₉ proximate the object side 120 and a surface S₁₀ distal the objectside. In this embodiment, surface S₉ has a radius of curvature ofapproximately 50 mm, while surface S₁₀ has a radius of curvature ofapproximately −50 mm. Thus, lens L₅, in this embodiment, is a bi-convexlens and may be considered a perfect bi-convex lens. Surfaces S₉ and S₁₀are both coated with approximately 0.5876 μm of Ar, although othersuitable coatings (or no coating at all) may be employed, as the presentinvention is not limited in this respect. The thickness, d₉, of lens L₅is approximately 1.47 mm. Lens L₅ also has a circular diameter D₅ ofapproximately 8 mm. The index of refraction, n₅, is approximately 1.744,while the dispersion, v₅, is approximately 44.72. Lens L₅ is a crownglass. It should be appreciated that the present invention is notlimited in this respect, as other suitable materials and/or othersuitable indices of refraction and/or dispersion may be employed.

Referring again to FIG. 1, it may be necessary to control the distancesbetween elements of the lens assembly 100. The distance between surfaceS₂ of lens L₁ and surface S₃ of lens L₂ is designated by d₂. Thedistance between surface S₅ of lens L₃ and surface S₆ of aperture stop106 is designated by d₅. The distance from surface S₆ of aperture stop106 to surface S₇ of lens L₄ is designated by d₆. The distance fromsurface S₈ of lens L₄ to surface S₉ of lens L₅ is designated by d₈. Thedistance from surface S₁₀ of lens L₅ to surface S₁₁ of planar plate F₁is designated by d₁₀. The distance from surface S₁₂ of planar plate F₁to surface S₁₃ of planar plate F₂ is designated by d₁₂. The distancefrom surface S₁₄ of planar plate F₂ to the image plane 122 isrepresented by d₁₄. Such distances are listed, for example, in Table 3.

According to one aspect of the invention a housing may be provided tohold the lenses and aperture stop of the lens assembly 100, and toensure that the values of d₂, d₅, d₆, and d₈ are maintainedappropriately. FIG. 6 shows an example of a side view of a housing 610in the absence of the lenses L₁-L₅.

In one embodiment, as shown in FIG. 6, the housing 610 contains housingsteps hs₁-hs₉. The housing steps are formed in the housing for thepurpose of receiving the lenses L₁-L₅ and ease the process of assemblingthe lenses L₁-L₅. Each housing step has a thickness, measured in thex-direction. The housing 610 is also circular, into and out of the page,so that each housing step has a diameter, measured in the y-direction.The approximate values of the housing step thicknesses and diameters areshown in Table 1. Note that in some instances the housing step has avariable diameter (i.e., is tapered) in which case the minimum diameteris listed. The total length T_(L) of the housing is approximately 16.1mm and the outer thread diameter O_(d) is approximately 14 mm. Thenon-threaded diameter Id of the housing at the portion 612 isapproximately 12 mm. It should be appreciated that the dimensions of thehousing are non-limiting. TABLE 1 Housing Step Sizes For FIG. 6 HousingStep Step Thickness (mm) Step Diameter (mm) hs₁ 0.43 11.00  hs₂ 0.6410.02  hs₃ 1.69 9.50 hs₄ 4.5 8.52 hs₅ 0.62 6.02 hs₆ 4.32 7.11 hs₇ 0.638.02 hs₈ 0.47 9.00 hs₉ 0.35  9.00**The listed value corresponds to the minimum diameter of the housingstep.

The housing 610 may be formed with threads 616 to allow the housing tobe threaded in and held relative to another component, such as a camerahousing. Specifically, an outer surface of the housing has threads. Inone embodiment, the housing is formed with an M14 thread, having, e.g.,an outer diameter of approximately 14.0 mm and a pitch diameter ofapproximately 13.5 mm. Of course, other suitable thread configurationsor other suitable attaching arrangements may be employed, as the presentinvention is not limited in this respect. The housing also has anon-threaded portion 612 of the outer surface to mate to a lensretainer, as described below in connection with FIGS. 8A and 8B.

In the illustrated embodiment a fixed aperture stop 606 is provided. Theaperture stop is an f4 stop with a diameter of approximately 4.52 mm.The thickness of the stop is approximately 0.2 mm. In another embodimentthe aperture stop may be variable. In another embodiment, the aperturestop may be provided by micro-plates that may take one of several sizes,with the micro-plate being held in the housing by any suitablemechanism. In one embodiment, the micro-plate may be held by at leastone of the lens elements.

The housing 610 may also be constructed to limit the amount ofinternally reflected light incident on the detector or imaging media. Inone embodiment, the housing includes an anti-halation region 614 ofapproximately 2.79 mm in thickness and 5.2 mm in diameter. Theanti-halation region may be formed as threads and functions to alter thereflection of light within the housing from what it would otherwise beif the threading were not provided, i.e., from a flat surface. Thisaffords certain optical benefits, such as reduced ghosting. Otherarrangements for reducing reflections may be employed, as the presentinvention is not limited in this respect.

In one embodiment, the housing 610 is formed of metal. However, itshould be appreciated that the housing could be formed out of anymaterial, including plastics, ceramics, or any other type of material,as the invention is not limited in this regard.

FIG. 7 shows the housing 610 of FIG. 6 with the lenses L₁-L₅ of FIG. 1disposed in the housing steps. Lens L₁ is disposed in housing step hs₂.Lenses L₂ and L₃ are disposed in housing step hs₄, which abuts theaperture stop 606. Lens L₄ is disposed in hs₅. Lens L₆ is disposed inhs₇. The lenses may fit snugly into the housing steps, or may be fixedwithin the housing steps by any suitable arrangement, for example, glue.By using the step locations in the housing, the lenses are spacedappropriately to ensure proper function of the lens assembly. Thedistances d₂, d₅, d₆, and d₈ are maintained at appropriate values.

To hold lens L₁ in place, in one embodiment as shown in FIG. 7, a lensretainer 702 is mated to the non-threaded portion 612 of the housing.The lens retainer 702 may be attached to the housing body using anysuitable arrangement, such as welding, adhesively bonding, threading,interference fitting (e.g., press or shrink fitting), etc. as thepresent invention is not limited in this respect. The lens retainer 702is illustrated in FIGS. 8A and 8B. FIG. 8A shows a front-on view of thelens retainer 702. FIG. 8B is a side view of the lens retainer 702. Asshown in FIG. 8B, the lens retainer has an inner mating surface with adiameter of approximately 12 mm, allowing it to mate with thenon-threaded portion 612 of housing 610.

To facilitate installing the housing to another component, the housingmay be formed with wrench flats. In one embodiment, the wrench flats areformed on the housing itself. In anther embodiment, the wrench flats areformed on the retainer. Thus, when the lens retainer 702 is mated to thenon-threaded portion 612 of housing 610, the wrench flats facilitatethreading the housing to the other component. The width across thewrench flats is approximately 13 mm. Other suitable arrangements tofacilitate threading the housing, such as, e.g., spanner wrench slotsmay be employed, as the present invention is not limited in thisrespect. The lens retainer has an inner diameter of approximately 9 mm.

Until this point, the discussion of the lenses in FIGS. 2-6 haspertained to an embodiment in which the lens assembly 100 is scaled foruse with a 1/2 inch CCD detector. However, as mentioned, the lensassembly may be scaled for use with other components, detectors, filterplates, or for any other reason, and in general the lens assembly 100may be scaled to any desired focal length. As an example, the lensassembly 100 may be scaled for use with a 1/3 inch CCD detector, asopposed to the 1/2 inch CCD detector described thus far. In thisembodiment, the lens assembly may be scaled to a focal length, f, ofapproximately 22.4 mm. The values for radii of curvature, index ofrefraction, dispersion, and spacing of elements may need to change toadapt the design to provide the desired optical performance with the 1/3inch CCD detector. The following description of the lenses in FIGS. 2-6pertains to an embodiment in which the lens assembly 100 is scaled foruse with a 1/3 inch CCD detector.

In this embodiment, surface S₁ has a radius of curvature ofapproximately 10.3 mm, while surface S₂ has a radius of curvature ofapproximately 85 mm. Surfaces S₁ and S₂ are both coated withapproximately 0.5876 μm of Ar, although other suitable coatings (or nocoating at all) may be employed, as the present invention is not limitedin this respect. The thickness, d₁, of lens L₁ is approximately 1.4 mm.Lens L₁ also has a circular diameter D₁ of approximately 7.5 mm. Theindex of refraction, n₁, is approximately 1.487, while the dispersion,v₁, is approximately 84.47. Lens L₁ is a crown glass. It should beappreciated that the present invention is not limited in this respect,as other suitable materials and/or other suitable indices of refractionand/or dispersion may be employed.

In this embodiment, surface S₃ of lens L₂ has a radius of curvature ofapproximately 6.27 mm. Common surface S₄ in this embodiment has a radiusof curvature of approximately 3.72 mm. Thus, the thickness d₃ of lens L₂is approximately 1.73 mm. Lens L₂ is circular with a diameter D₂ ofapproximately 6.5 mm. Lens L₂ has an index of refraction, n₂, ofapproximately 1.805 and a dispersion, v₂, of approximately 25.36. LensL₂ is a flint glass. It should be appreciated that the present inventionis not limited in this respect, as other suitable materials and/or othersuitable indices of refraction and/or dispersion may be employed.

Lens L₃ has a surface S₅ with a radii of curvature of approximately 4.35mm, such that the thickness d₄ of lens L₃ is approximately 2.6 mm. LensL₃ also has a circular diameter D₃ of approximately 6.5 mm. Lens L₃ hasan index of refraction, n₃, of approximately 1.620 and a dispersion, v₃,of approximately 60.32. Lens L₃ is a crown glass. It should beappreciated that the present invention is not limited in this respect,as other suitable materials and/or other suitable indices of refractionand/or dispersion may be employed.

Surface S₃ of lens L₂, and surface S₅ of lens L₃ are coated withapproximately 0.5876 μm of Ar, although other suitable coatings (or nocoating at all) may be employed, as the present invention is not limitedin this respect. It is also seen in FIG. 3 that lenses L₂ and L₃ arecemented together. This may be accomplished by any suitable means, forexample, UV epoxy.

In this embodiment, lens L₄ of FIG. 4 has a surface S₇ having a radiusof curvature of approximately −5.541 mm, while surface S₈ has a radiusof curvature of approximately −7.0 mm. Surfaces S₇ and S₈ are bothcoated with approximately 0.5876 μm of Ar, although other suitablecoatings (or no coating at all) may be employed, as the presentinvention is not limited in this respect. The thickness, d₇, of lens L₄is approximately 1.00 mm. Lens L₄ also has a circular diameter D₄ ofapproximately 5 mm. Lens L₄ has an index of refraction, n₄, ofapproximately 1.717, while the dispersion, v₄, is approximately 47.96.Lens L₄ is a crown glass. It should be appreciated that the presentinvention is not limited in this respect, as other suitable materialsand/or other suitable indices of refraction and/or dispersion may beemployed.

In this embodiment, surface S₉ of lens L₅ has a radius of curvature ofapproximately 37 mm. Surface S₁₀ has a radius of curvature ofapproximately −37 mm. Thus, lens L₆ in this embodiment is a bi-convexlens and may be considered a perfect bi-convex lens. Surfaces S₉ and S₁₀are both coated with approximately 0.5876 μm of Ar, although othersuitable coatings (or no coating at all) may be employed, as the presentinvention is not limited in this respect. The thickness, d₉, of lens L₅is approximately 1.50 mm. Lens L₅ also has a circular diameter D₅ ofapproximately 6.5 mm. The index of refraction, n₅, is approximately1.744, while the dispersion, v₅, is approximately 44.72. Lens L₅ is acrown glass. It should be appreciated that the present invention is notlimited in this respect, as other suitable materials and/or othersuitable indices of refraction and/or dispersion may be employed.

In this embodiment, the housing 610 may no longer be adequate to holdthe lenses L₁-L₅. Therefore, a housing 910 may be provided, as shown inFIG. 9, which is a cross-section view of housing 910 in the absence oflenses L₁-L₅.

In one embodiment, the housing 910 includes housing steps hs₁₀-hs₂₂. Thehousing steps are formed in the housing for the purpose of receiving thelenses L₁-L₅, and ease the process of assembling the lenses L₁-L₅. Eachhousing step has a thickness, measured in the x-direction. The housing910 is also circular, into and out of the page, so that each housingstep has a diameter, measured in the y-direction. The approximate valuesof the housing step thicknesses and diameters are shown in Table 2. Notethat in some instances the housing step has a variable diameter (i.e.,is tapered) in which case the minimum diameter is listed. The totallength TL of the housing is approximately 14.3 mm and the outer diameterO_(d) is approximately 9.5 mm. It should be appreciated that thedimensions of the housing are non-limiting. TABLE 2 Housing Step SizesFor FIG. 9 Housing Step Step Thickness (mm) Step Diameter (mm) hs₁₀ 0.25 8.75* hs₁₁ 0.25 8.75 hs₁₂ 0.60 8.22 hs₁₃ 0.40 8.00 hs₁₄ 0.50 7.52 hs₁₅1.50 7.00 hs₁₆ 3.50 6.52 hs₁₇ 0.79 5.02 hs₁₈ 1.15 5.50 hs₁₉ 1.84 6.00hs₂₀ 0.66 6.52 hs₂₁ 0.50 7.00 hs₂₂ 0.30  7.00**The listed value corresponds to the minimum diameter of the housingstep.

As with housing 610, housing 910 may be formed with threads 916 to allowthe housing to be threaded in and held relative to another component,such as a camera housing. Specifically, an outer surface of the housinghas threads. In one embodiment, the housing is formed with an M9 thread,having, e.g., an outer diameter of approximately 8.9 mm and a pitchdiameter of approximately 8.6 mm. Of course, other suitable threadconfigurations or other suitable attaching arrangements may be employed,as the present invention is not limited in this respect. Wrench flats912 may be formed along the length of the housing, or as shown, along aportion of the housing to facilitate threading the housing to the othercomponent. The width across the wrench flats is approximately 9 mm.Other suitable arrangements to facilitate threading the housing, suchas, e.g., spanner wrench slots may be employed, as the present inventionis not limited in this respect.

In the illustrated embodiment a fixed aperture stop 906 is provided. Theaperture stop is an f4 stop with a diameter of approximately 3 mm. Thethickness of the stop is approximately 0.2 mm. In another embodiment theaperture stop may be variable. In another embodiment, the aperture stopmay be provided by micro-plates that may take one of several sizes, withthe micro-plate being held in the housing by any suitable mechanism. Inone embodiment, the micro-plate may be held by at least one of the lenselements.

The housing 910 also has a anti-halation thread region 914 ofapproximately 1.86 mm in thickness and 4.5 mm in diameter. Theanti-halation region may be formed as threads and functions to alter thereflection of light within the housing from what it would otherwise beif the threading were not provided, i.e., from a flat surface. Thisaffords certain optical benefits, such as reduced ghosting. Otherarrangements for reducing reflections may be employed, as the presentinvention is not limited in this respect.

In one embodiment, the housing 910 is formed of metal. However, itshould be appreciated that the housing could be formed out of anymaterial, including plastics, ceramics, or any other type of material,as the invention is not limited in this regard.

FIG. 10 shows the housing 910 of FIG. 9 with the lenses L₁-L₅ of FIG. 1disposed in the housing steps. Note that in this Figure the housing 910is rotated so that wrench flats 912 are not visible. Lens L₁ is disposedin housing step hs₂. Lenses L₂ and L₃ are disposed in housing step hs₄,which abuts the aperture stop 906. Lens L₄ is disposed in hs₅. Lens L₆is disposed in hs₇. The lenses may fit snugly into the housing steps, ormay be fixed within the housing steps by any suitable means, forexample, glue. By using the step locations in the housing, the lensesare spaced appropriately to ensure proper function of the lens assembly.In other words, the distances d₂, d₅, d₆, and d₈ are maintained atappropriate values.

A lens retainer 1002 is disposed in housing step hs₁₂ to hold lens L₁ inplace. The lens retainer 1002 is illustrated in FIGS. 11A and 11B. Asseen in FIG. 11A, which is a front-on view of the lens retainer, thelens retainer 1002 has an outer circular diameter of approximately 8.2mm, and an inner circular diameter of approximately 6.75 mm.

FIG. 11B is a side view of the lens retainer 1002. As shown, the lensretainer has an approximate thickness of 1 mm. The lens retainer may fitsnugly in the housing step hs₁₂. The lens retainer 1002 may be attachedto the housing body using any suitable arrangement, such as welding,adhesively bonding, threading, interference fitting (e.g., press orshrink fitting), etc. as the present invention is not limited in thisrespect.

Tables 3 and 4 provide the prescription for lens assemblies according toembodiments in which the lens assembly of FIG. 1 is scaled to a focallength of approximately 25 mm. Again, the values shown in these tablescould be scaled to provide a lens assembly having a different focallength. Such scaling of values is meant to be encompassed by the presentinvention. TABLE 3 Prescription 1 For Lens Assembly of FIG. 1 with f =25 mm Radius of Curvature r Thickness d Refractive Index Abbe No.Surface (mm) (mm) (n) (ν) S₁ 11.399 1.563 1.487 84.47 S₂ 95.674 0.260 S₃6.926 1.931 1.805 25.36 S₄ 4.107 2.902 1.620 60.32 S₅ 4.777 0.586 S₆Aperture 2.935 S₇ −6.393 1.116 1.717 47.96 S₈ −8.404 2.319 S₉ 38.5231.674 1.744 44.72 S₁₀ −38.523

TABLE 4 Prescription 2 For Lens Assembly of FIG. 1 with f = 25 mm Radiusof Curvature r Thickness d Refractive Index Abbe No. Surface (mm) (mm)(n) (ν) S₁ 9.943 1.546 1.487 84.47 S₂ 55.798 0.204 S₃ 6.028 1.034 1.80525.36 S₄ 4.097 2.930 1.620 60.32 S₅ 4.249 0.650 S₆ Aperture 2.934 S₇−5.196 0.930 1.717 47.96 S₈ −6.572 1.682 S₉ 47.134 1.277 1.744 44.72 S₁₀−47.134

According to another embodiment, the lens assembly may take the form oflens assembly 1200 illustrated in FIG. 12. Note that in this figure thelenses and lens surfaces are labeled to correspond to the labels in FIG.1, for purposes of simplification.

In this embodiment, lens assembly 1200 includes five lenses, L₁-L₅,disposed between an object side 1220 and an image plane 1222. In thisembodiment, lens L₁ is a plano-convex lens. Lenses L₂ and L₃ aremeniscus lenses and are cemented together. Lens L₄ is a bi-concave lens,and may be considered a perfect bi-concave lens. Lens L₅ is a bi-convexlens, and may be a considered a perfect bi-convex lens. An aperture stop1206 is disposed between lens L₃ and lens L₄.

Tables 5-12 provide prescriptions for the lens assembly 1200 thatconform to the general structure illustrated in FIG. 12. The embodimentsof Tables 5-12 are scaled to a focal length of f=25. The values listedcould be scaled to an alternative focal length, as would be known to oneof skill in the art, and such scaling does not depart from the spirit ofthe invention. TABLE 5 Prescription 1 For Lens Assembly of FIG. 12 withf = 25 mm Radius of Curvature r Thickness d Refractive Index Abbe No.Surface (mm) (mm) (n) (ν) S₁ 13.047 1.500 1.487 70.41 S₂ Infinity 0.206S₃ 6.863 1.930 1.805 25.36 S₄ 3.881 2.919 1.589 61.27 S₅ 5.517 0.586 S₆Aperture 1.331 S₇ −22.928 1.023 1.517 64.17 S₈ 12.188 1.330 S₉ 22.1731.631 1.744 44.72 S₁₀ −22.173

TABLE 6 Prescription 2 For Lens Assembly of FIG. 12 with f = 25 mmRadius of Curvature r Thickness d Refractive Index Abbe No. Surface (mm)(mm) (n) (ν) S₁ 13.899 1.414 1.487 70.41 S₂ Infinity 0.203 S₃ 6.1761.659 1.805 25.36 S₄ 3.714 3.289 1.589 61.27 S₅ 4.525 0.586 S₆ Aperture2.933 S₇ −15.249 1.006 1.517 64.17 S₈ 118.872 2.126 S₉ 28.563 1.4251.744 44.72 S₁₀ −28.563

TABLE 7 Prescription 3 For Lens Assembly of FIG. 12 with f = 25 mmRadius of Curvature r Thickness d Refractive Index Abbe No. Surface (mm)(mm) (n) (ν) S₁ 14.868 1.563 1.487 70.41 S₂ Infinity 0.260 S₃ 6.7371.931 1.805 25.36 S₄ 3.906 2.902 1.589 61.27 S₅ 5.393 0.586 S₆ Aperture2.935 S₇ −22.650 1.116 1.517 64.17 S₈ 15.203 1.045 S₉ 20.707 1.674 1.71747.96 S₁₀ −20.707

TABLE 8 Prescription 4 For Lens Assembly of FIG. 12 with f = 25 mmRadius of Curvature r Thickness d Refractive Index Abbe No. Surface (mm)(mm) (n) (ν) S₁ 13.128 1.429 1.487 70.41 S₂ Infinity 0.200 S₃ 6.6331.930 1.805 25.36 S₄ 3.812 2.954 1.589 61.27 S₅ 4.977 0.586 S₆ Aperture2.903 S₇ −20.549 1.007 1.517 64.17 S₈ 17.262 1.811 S₉ 21.847 1.640 1.71747.96 S₁₀ −21.847

TABLE 9 Prescription 5 For Lens Assembly of FIG. 12 with f = 25 mmRadius of Curvature r Thickness d Refractive Index Abbe No. Surface (mm)(mm) (n) (ν) S₁ 13.633 1.563 1.487 70.41 S₂ Infinity 0.260 S₃ 6.7941.931 1.805 25.36 S₄ 3.865 2.902 1.607 56.65 S₅ 5.094 0.586 S₆ Aperture2.935 S₇ −24.337 1.116 1.517 64.17 S₈ 24.337 2.319 S₉ 24.948 1.674 1.71747.96 S₁₀ −24.948

TABLE 10 Prescription 6 For Lens Assembly of FIG. 12 with f = 25 mmRadius of Curvature r Thickness d Refractive Index Abbe No. Surface (mm)(mm) (n) (ν) S₁ 13.957 1.417 1.487 70.41 S₂ Infinity 0.203 S₃ 6.4781.725 1.805 25.36 S₄ 3.776 3.176 1.607 56.65 S₅ 4.817 0.586 S₆ Aperture2.934 S₇ −19.451 1.013 1.517 64.17 S₈ 19.451 1.381 S₉ 22.012 1.605 1.71747.96 S₁₀ −22.012

TABLE 11 Prescription 7 For Lens Assembly of FIG. 12 with f = 25 mmRadius of Curvature r Thickness d Refractive Index Abbe No. Surface (mm)(mm) (n) (ν) S₁ 14.878 1.563 1.517 64.17 S₂ Infinity 0.260 S₃ 6.7961.931 1.805 25.36 S₄ 3.872 2.902 1.620 60.32 S₅ 5.072 0.586 S₆ Aperture2.935 S₇ −24.452 1.116 1.487 70.41 S₈ 24.452 2.319 S₉ 25.942 1.674 1.71747.96 S₁₀ −25.942

TABLE 12 Prescription 8 For Lens Assembly of FIG. 12 with f = 25 mmRadius of Curvature r Thickness d Refractive Index Abbe No. Surface (mm)(mm) (n) (ν) S₁ 14.813 1.358 1.517 64.17 S₂ Infinity 0.205 S₃ 6.6751.879 1.805 25.36 S₄ 3.809 3.104 1.620 60.32 S₅ 4.894 0.586 S₆ Aperture2.931 S₇ −21.412 1.020 1.487 70.41 S₈ 21.412 1.905 S₉ 24.205 1.559 1.71747.96 S₁₀ −24.205

According to another embodiment, the lens assembly may take the form oflens assembly 1300 illustrated in FIG. 13. In this embodiment, lensassembly 1300 includes five lenses, L₁-L₅, disposed between an objectside 1320 and an image plane 1322. In this embodiment, lens L₁ isplano-convex lens. Lenses L₂ and L₃ are meniscus lenses, and arecemented together. Lens L₄ is a meniscus lens having negative radii ofcurvature. Lens L5 is a bi-convex lens, and may be a considered aperfect bi-convex lens. An aperture stop 1306 is disposed between lensL₃ and lens L₄.

Tables 13 and 14 provide prescriptions of the elements of the lensassembly 1300 that conform to the general form illustrated in FIG. 13.The values listed could be scaled to an alternative focal length, aswould be known to one of skill in the art, and such scaling does notdepart from the spirit of the invention. TABLE 13 Prescription 1 ForLens Assembly of FIG. 13 with f = 25 mm Radius of Curvature r Thicknessd Refractive Index Abbe No. Surface (mm) (mm) (n) (ν) S₁ 13.279 1.5631.487 84.47 S₂ Infinity 0.260 S₃ 6.606 1.931 1.805 25.36 S₄ 3.920 2.9021.620 60.32 S₅ 4.569 0.586 S₆ Aperture 2.155 S₇ −9.710 1.116 1.717 47.96S₈ −16.572 2.935 S₉ 32.767 1.674 1.744 44.72 S₁₀ −32.767

TABLE 14 Prescription 2 For Lens Assembly of FIG. 13 with f = 25 mmRadius of Curvature r Thickness d Refractive Index Abbe No. Surface (mm)(mm) (n) (ν) S₁ 11.067 1.637 1.487 84.47 S₂ Infinity 0.207 S₃ 5.7710.875 1.805 25.36 S₄ 4.070 2.576 1.620 60.32 S₅ 4.078 0.750 S₆ Aperture0.591 S₇ −10.275 0.900 1.717 47.96 S₈ −16.300 2.931 S₉ 47.056 1.3001.744 44.72 S₁₀ −47.056

According to another embodiment, the lens assembly may take the formshown in FIG. 14. In this embodiment, lens assembly 1400 includes fivelenses, L₁-L₅, disposed between an object side 1420 and an image plane1422. Lens L₁ is meniscus lens having positive radii of curvature.Lenses L₂ and L₃ are meniscus lenses having positive radii of curvatureand are cemented together. Lens L₄ is a bi-concave lens, and may beconsidered a perfect bi-concave lens. Lens L₅ is a bi-convex lens, andmay be considered a perfect bi-convex lens. An aperture stop 1406 isdisposed between lens L₃ and lens L₄.

In a more general sense, the design of the lens assemblies describedthus far, according to the present invention, may obey any, all, or anycombination of the relationships shown in Table 15. For purposes of thistable, f represents the effective focal length of the lens assembly. Thefocal length of the individual lens elements is represented by f₁, f₂,etc. The focal length of the doublet including lenses L₂ and L₃ isrepresented by f₂, f₃. The radii of curvature for the respectivesurfaces are labeled as r₁, r₂, etc. In Table 15, the indices ofrefraction for the respective lens elements are represented by thenotation n₁, n₂, etc, and the values of dispersion for the respectivelens elements by v₁, v₂, etc. It should also be noted that for certainlistings in table 15 the values correspond to a lens assembly scaled toan effective focal length f=25 mm. These relationships listings areclearly designated in Table 15, and it should be appreciated that thecorresponding values may be scaled if the lens assembly is scaled to analternative focal length. TABLE 15 Ratios and Relationships For LensAssembly 0.98 * f < d₁ + d₂ + d₃ + d₄+ d₅ + d₆ + d₇ + d₈ + d₉ + d₁₀ +d₁₁ + d₁₂ + d₁₃+ d₁₄ < 1.02 * f 0.47 * f < d₁ + d₂ + d₃ + d₄+ d₅ + d₆ +d₇ + d₈ + d₉ < 0.61 * f 20.4 mm < f₁ < 30.5 mm when assembly scaled to f= 25 mm −100 mm < f_(2,3) < 15 mm when assembly scaled to f = 25 mm 1.49< n₁ < 1.52 and ν₁ > 70 1.8 < n₂ and 24 < ν₂ < 26 −50 mm < f₄ < −35 mmwhen 1.5 < n₄ < 1.72 and when assembly scaled to f = 25 mm 110 mm < f₅ <540 mm when n₅ > 1.7 and when assembly scaled to f = 25 mm r₇/r₁₀ < 0.3when n₄/n₅ > 0.98 r₇/r₁₀ > 0.5 when n₄/n₅ < 0.90

As discussed above, an aspect of the present application providescorrection for coma and astigmatism, as well as any other aberrationsthat may be introduced by using plane parallel plates with a lensassembly, for example, any of the lens assemblies 100, 1200, 1300, and1400. According to one embodiment, the lens assembly includescompensating aberrations to compensate the aberrations of plane parallelplates. FIG. 15 is a non-limiting example of values of Seidel aberrationcoefficients, in units of waves, at a wavelength of 0.5876 μm for seventypes of aberrations that may be introduced in the lens assemblyaccording to the present invention. Values are listed for each of thesurfaces S₁-S₁₄, as well as for the image itself, which in this exampledoes not contribute any non-zero values. The seven types of aberrationslisted are spherical aberration (W040), coma (W131), astigmatism (W222),field curvature (W220), distortion (W311), longitudinal chromaticaberration (W020), and tangential chromatic aberration (W111).

The total values listed for each type of aberration are computed by asum of the value for each surface as well as the value for the imageitself. The aperture stop (surface S₆) and the image do not contributeto the seven listed types of aberrations of the system, as indicated bythe values of zero in the appropriate rows. As indicated by the totalvalues in FIG. 15, satisfactory optical performance may be retained evenwith the planar plates. In this non-limiting example, the Petzval radiusis −704.0739.

As previously mentioned, in some embodiments, the lens assembliesprovide less than 1% distortion. Many waves of distortion in the exitpupil may be required to produce 1% error in the image height relativeto the full field image height. Distortion at any one field may appearto be similar to tilt. Distortion without deteriorating the imagequality of a point image may occur With respect to FIG. 15, the detailsfor converting from waves to percent distortion are:

W311 is the distortion coefficient in waves at the full field, and fullpupil. At the full field, W311*p describes the wavefront in the ydirection, which resembles a tilted wavefront relative to the idealreference wavefront. The tilted wavefront at full field forms an anglerelative to the reference wavefront in the exit pupil. A ray projectednormal from the wavefront will land on the image plane with some heightrelative to the height of a ray from the reference wavefront. Thedifference in ray height is ey. Distortion is then computed by dividingey by the height of the nominal full field image height, which can beobtained from a paraxial ray trace.

In general: e_(y)=−(R*lambda)/n*(W)′

For distortion: e_(y)=−(R*lambda)/n*(W311*p)′ where (W311*p)′ is thederivative of (W311*p) with respect to y, and R is the distance from theexit pupil to the image plane. This reduces toe _(y)=−(R*lambda)/(n*Y max_pupil)*W 311.

After rearranging terms this is equal to the expression for transversedistortione _(y)=−(R/Y max_pupil)*(lambda/n)*W 311e _(y)=(lambda*W 311)/(n′u′)where u′ is the image space paraxial marginal ray angle.

Lastly, percent distortion is computed with the following using e_(y).Percent distortion: Dist=(e _(y) /Yc)*100%where Yc is the paraxial chief ray height.

An example of the numbers for a lens assembly according to the presentinvention, when scaled for use with a 1/3 inch CCD detector are nowgiven, specifically using the total value of W311 from FIG. 15:using e _(y)=(lambda*W 311)/(n′u′) (or the other equation)e _(y)=(0.5876E-3 mm*−4.858511)/(−0.1175)e _(y)=0.02429 mmdistortion=0.02429 mm/3.0485 mm*100%distortion=0.797%

The percent distortion computed with real rays relative to the scaledimage height from a very small field at wavelength no. 2 (which iscalled the primary wavelength, in ZEMAX, an optical design program) is0.793%, and therefore less than 1%.

As described above, another aspect of the invention relates to amulti-head imaging device for imaging an object. As shown schematicallyin FIG. 16, the multi-head imaging device 1602 includes two distinctlens assemblies, 1604 and 1606, that may be identical to each other ordifferent from each other. Each lens assembly is associated with adistinct detector, 1608 and 1610, respectively. The detector may be aCCD, CMOS, film-based or any suitable combination thereof. Of courseother types of detectors may be employed, as the present invention isnot limited in this respect.

The multi-head imaging device may include any suitable lens assembly asdesired, to produce a desired image of the object. Although the lensassemblies may be identical to each other or otherwise produce anidentical or similar result, in one embodiment, one lens assembly is aconstant focus lens assembly. In one embodiment, one of the lensassemblies is a wide-angle lens assembly. In another embodiment, onelens assembly is a 40 degree field of view lens, such as that describedin co-pending U.S. patent application Ser. No. 10/798,841, assigned tothe assignee of the present application and hereby incorporated byreference in its entirety. Other suitable wide angle lens assemblies maybe employed, as the present invention is not limited in this respect.Similarly, any of the lens assemblies described herein or in the '841application may be employed. In one embodiment, one of the lensassemblies is a 15 degree field of view lens. In another embodiment, oneof the lens assemblies is a relatively high magnification lens or atelephoto or moderate telephoto lens assembly, for example, a lensassembly providing approximately a 10× magnification.

As shown in FIG. 17, the multi-head imaging device 1602 includes ahousing 1610 adapted to receive the lens assemblies 1604, 1606. In oneembodiment, the housing 1610 includes receptacles 1612, 1614, eachconfigured to receive a respective one of the lens assemblies. Tofacilitate holding the lens assemblies in the housing, the receptaclesmay be threaded with a thread corresponding to the threaded housings ofthe lens assemblies as described with reference to FIGS. 6-11.

In one embodiment, the lens assemblies are positioned in the housing ofthe multi-head imaging device in a manner such that the optical viewingaxes of the lens assemblies are substantially parallel. Of course, thepresent invention is not limited in this respect, as the axes need notbe parallel.

The housing 1610 may be formed as an integral unitary construction ormay be constructed with two or more components joined together. In oneembodiment, the housing comprises a lens assembly housing componentconstructed to receive the lens assemblies as described above and a backplate component that covers the back side of the housing 1610. Byproviding such a two piece construction, disposing the detectors withinthe housing 1610 may be facilitated. Of course, the present invention isnot limited in this respect, as additional components may be employed toform the housing 1610.

In one embodiment, the housing 10 has a width (w) of approximately 1.4inches, a height (h) of approximately 0.57 inches, and a depth (d1) ofapproximately 0.9 inches and a depth (d2) of approximately 0.52 inches.Thus, in one embodiment, the housing 1610 fits within an envelope ofapproximately 1.5 inch by 0.75 inch by 1 inch. Of course, the presentinvention is not limited in this respect, as the housing may be formedwith any suitable size.

The multi-head imaging device may be mounted to a motion assembly 1620,as shown in FIGS. 16 and 17 to provide the ability to move themulti-head imaging device in a desired orientation. In one embodiment,the multi-head imaging device is mounted to a mount that provides panand tilt motion. This may be provided with the use of a gear arrangement1622, shaft 1624 and yoke 1626, as shown. However, other suitablearrangements for providing motion may be employed, as the presentinvention is not limited in this respect. The pan/tilt mount 1620 may becoupled to a control assembly 1630. The control assembly controls themovement and/or function of the dual-head assembly 1602.

Although not shown, a housing cover, which may be formed as a dome, maybe employed, whereby the lens assemblies are able to view the objectthrough the dome. The dome may be made of glass, plastic, or any othersuitable material, and the invention is not limited in this respect. Inone embodiment, the dome is optically clear.

According to one embodiment, a user may view an image provided by one ofthe two distinct lens assemblies. The user may choose which lensassembly through which to view an object and may switch lens assembliesthrough which to view the object, as desired. Thus, a user may manuallyswitch between lens assemblies. Alternatively, or in addition, switchingbetween views may occur automatically and may be programmed orcontrolled by software. In one embodiment, switching between lensassemblies may occur in response to a trigger event (which may be aprogrammed event or a detected event). In one embodiment, switchingbetween lens assemblies may occur upon motion occurring in the field ofview or a predetermined object in or entering the field of view. In oneembodiment, switching between views may occur instantaneously.

For example, initially an image produced by lens assembly 1606 may beviewed. Upon detecting motion, or an object of interest in the field ofview of lens assembly 1606, a switch may occur to enable viewing animage produced by lens assembly 1604. The motion, movement, andoperation of the dual-head assembly 1602 may be controlled by a user, acomputer, or any other means, as the invention is not limited in thisrespect.

Although certain embodiments are described as including only two lensassemblies, the present invention is not limited in this respect, asadditional lens assemblies may be provided in a multi-lens assemblyhead.

The lens assemblies described herein may be used in various applicationsand environments. For example, one field of use may be security cameras.Security cameras may be used in banks, casinos, retail stores, personalproperty, yards, airports, sports and entertainment arenas, theaters,restaurants, cars, office buildings, gas stations, security checkpoints,boarder or other boundary crossings, transportation vehicles andterminals, such as trains and train stations, ships and docks, buses andbus depots, military installations, etc. as the present invention is notlimited in this respect.

The lens assemblies described herein may also be used for industrialapplications. Examples of this sort of use may include flexible borescopes with a distal chip, cameras for insertion into wells, cameras forviewing engines (such as aircraft engines) and engine parts, cameras forviewing under buildings or cars, cameras used for measurement, or anyother industrial application. The lens assemblies described herein mayalso be used for personal or business applications. Examples of thissort may include personal cameras, digital cameras, phone cameras, webcameras, disposable cameras, videography, or any other type of camera orsystem.

The lens assemblies described herein may also be used for personal orbusiness applications. Examples of this sort may include personalcameras, digital cameras, phone cameras, web cameras, disposablecameras, videography, or any other type of camera or system.

The lens assemblies described herein may also be used for medicalapplications. For example, the lens assemblies may be used for endoscopywith a distal chip, dental procedures, gynecological exams,ear/nose/throat exams, distal chip colonoscopy, distal chip laparoscopy,or any other medical procedures or uses.

Other applications will be readily apparent to those of skill.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Further, although each embodiment described aboveincludes certain features, the invention is not limited in this respect.Thus, one or more of the above-described or other features of the lensassembly, may be employed singularly or in any suitable combination, asthe present invention is not limited to a specific embodiment.Accordingly, the foregoing description and drawings are by way ofexample only.

1. A lens assembly comprising, in order from an object side to an image side: a first lens; a first meniscus lens in optical communication with the first lens; a second meniscus lens in optical communication with the first meniscus lens; an aperture stop in optical communication with the second meniscus lens; a fourth lens in optical communication with the aperture stop; and a bi-convex lens in optical communication with the fourth lens.
 2. The lens assembly of claim 1, wherein the first lens is a meniscus lens and the fourth lens is a meniscus lens.
 3. The lens assembly of claim 2, wherein the second meniscus lens and the third meniscus lens are cemented together.
 4. The lens assembly of claim 2, wherein the bi-convex lens is a perfect bi-convex lens.
 5. The lens assembly of claim 1, wherein the first lens is a plano-convex lens and the fourth lens is a meniscus lens.
 6. The lens assembly of claim 5, wherein the second meniscus lens and the third meniscus lens are cemented together.
 7. The lens assembly of claim 5, wherein the bi-convex lens is a perfect bi-convex lens.
 8. The lens assembly of claim 1, wherein the first lens is a meniscus lens and the fourth lens is a bi-concave lens.
 9. The lens assembly of claim 8, wherein the second meniscus lens and the third meniscus lens are cemented together.
 10. The lens assembly of claim 8, wherein the bi-convex lens is a perfect bi-convex lens.
 11. The lens assembly of claim 1, wherein the first lens is a plano-convex lens and the fourth lens is a bi-concave lens.
 12. The lens assembly of claim 11, wherein the second meniscus lens and the third meniscus lens are cemented together.
 13. The lens assembly of claim 11, wherein the bi-convex lens is a perfect bi-convex lens.
 14. The lens assembly of claim 1, further comprising at least one planar plate in disposed between the object side and the image side.
 15. The lens assembly of claim 14, wherein the at least one planar plate includes one filter plate.
 16. The lens assembly of claim 15, wherein the at least one planar plate further include a cover glass to cover a detector.
 17. The lens assembly of claim 16, wherein the filter plate and the cover glass are disposed adjacent to each other.
 18. The lens assembly of claim 15, wherein the filter plate is a low-pass filter plate.
 19. The lens assembly of claim 15, wherein the filter plate is a color-correction filter plate.
 20. The lens assembly of claim 1, wherein the first lens includes a first surface proximate the object side, and the bi-convex lens includes a second surface distal the object side, and wherein a distance between the first surface and the second surface is less than approximately 20 mm.
 21. A lens assembly comprising: a plurality of lenses for producing an image of an object, the plurality of lenses adapted to provide: a field of view of approximately 15 degrees; approximately 0% vignetting within the field of view; and a distortion of the image of less than approximately 1%.
 22. The lens assembly of claim 21, wherein the plurality of lenses are configured to define a focal length, and wherein a length of the plurality of lenses is approximately equal to the focal length.
 23. The lens assembly of claim 21, further comprising: an aperture stop in optical communication with the plurality of lenses.
 24. The lens assembly of claim 23, wherein the plurality of lenses is non-symmetrical about the aperture stop.
 25. The lens assembly of claim 21, further comprising: at least one planar plate in optical communication with the plurality of lenses.
 26. The lens assembly of claim 25, wherein the plurality of lenses is further adapted to provide: offsetting aberrations to compensate for aberrations introduce by the at least one planar plate.
 27. The lens assembly of claim 21, wherein the plurality of lenses includes five lenses.
 28. The lens assembly of claim 27, wherein the five lenses include, in order from an object side to an image side: a first lens; a first meniscus lens; a second meniscus lens; a fourth lens; and a bi-convex lens.
 29. The lens assembly of claim 28, wherein the first lens is a plano-convex lens.
 30. The lens assembly of claim 28, wherein the first lens is a meniscus lens.
 31. The lens assembly of claim 28, wherein the fourth lens is a meniscus lens.
 32. The lens assembly of claim 28, wherein the fourth lens is a biconcave lens.
 33. An imaging device for imaging an object, the imaging device comprising: an imaging device housing; a plurality of individual lens assemblies disposed at least partially within the image device housing; and a plurality of detectors disposed at least partially within the image device housing, each detector optically arranged relative to a respective one of the lens assemblies to receive images from the respective lens assembly.
 34. The imaging device of claim 33, wherein the image device housing comprises a plurality of lens assembly receptacles, each adapted to receive a respective one of the plurality of lens assemblies.
 35. The imaging device of claim 33, wherein the plurality of lens assemblies comprises a first lens assembly and a separate second lens assembly.
 36. The imaging device of claim 33, wherein the plurality of lens assemblies comprises a first lens assembly and a separate second lens assembly and wherein the image device housing comprises a first lens receptacle adapted to receive the first lens assembly and a second lens receptacle adapted to receive the second lens assembly.
 37. The imaging device of claim 33, wherein each lens assembly of the plurality of lens assemblies is different, thereby providing a different image of the object.
 38. The imaging device of claim 33, wherein the plurality of detectors comprises: a CCD detector, a CMOS detector, a film-based detector, or any combination thereof.
 39. The imaging device of claim 33, wherein each lens assembly of the plurality of lens assemblies is arranged relative to the image device housing such that an optical viewing axis of each lens assembly is generally aligned.
 40. The imaging device of claim 33, further comprising a mount coupled to the image device housing, wherein the mount is constructed to provide pan and tilt motion.
 41. The imaging device of claim 33, wherein the image device housing comprises a one piece housing.
 42. The imaging device of claim 33, further comprising a manually operable switch adapted to allow a user to switch a view of the object between at least two of the plurality of lens assemblies.
 43. The imaging device of claim 33, further comprising a controller adapted to automatically switch a view of the object between at least two of the plurality of lens assemblies upon an occurrence of a pre-determined trigger event.
 44. The imaging device of claim 33, wherein the imaging device housing is constructed to fit within a 1.5 inch by 1 inch by 0.75 inch envelope.
 45. The imaging device of claim 33, wherein a first one of the plurality of lens assemblies comprises a lens assembly constructed to provide a relatively wide field of view of the object and a second one of the plurality of lens assemblies is constructed to provide a relatively magnified view of the object.
 46. The imaging device of claim 45, wherein the first lens assembly is constructed to provide approximately a 40 degree field of view.
 47. The imaging device of claim 45, wherein the second lens assembly is constructed to provide approximately a 15 degree field of view.
 48. The imaging device of claim 33, wherein each of the plurality of lens assemblies is disposed within a lens housing, with the lens housing fastened to the image device housing.
 49. The imaging device of claim 48, wherein the lens housing comprises a threaded body and wherein the image device housing comprises a threaded receptacle, wherein the lens housing is threaded into the receptacle.
 50. A lens assembly comprising: a first lens arrangement comprising at least one lens element having at least one initial parameter; and a second lens arrangement in optical communication with the first lens arrangement, the second lens arrangement comprising at least one lens element having at least one initial parameter, wherein the first and second lens arrangements cooperate to produce an image having an image characteristic within a range of acceptable image characteristics; wherein a first parameter of the at least one initial parameter of the first lens arrangement may be changed while maintaining one or more parameters of the at least one initial parameter of the second lens arrangement within a desired range so that the image characteristic is maintained within the range of acceptable image characteristics.
 51. The lens assembly of claim 50, wherein the one or more parameters of the at least one initial parameter of the second lens arrangement include a radius of curvature.
 52. The lens assembly of claim 51, wherein the radius is maintained within 10% of the initial radius of curvature.
 53. The lens assembly of claim 50, wherein the one or more parameters of the second lens arrangement include an index of refraction.
 54. The lens assembly of claim 53, wherein the index of refraction is maintained at a value substantially equal to the initial index of refraction.
 55. The lens assembly of claim 50, wherein the one or more parameters of the second lens arrangement include a value of dispersion.
 56. The lens assembly of claim 55, wherein the value of dispersion is maintained at a value substantially equal to the initial value of dispersion.
 57. The lens assembly of claim 50, wherein the first lens arrangement and second lens arrangement combined is a five lens element lens assembly
 58. The lens assembly of claim 57, wherein the first lens arrangement includes: a first lens; and a fourth lens.
 59. The lens assembly of claim 58, wherein the second lens arrangement includes: a second lens; a third lens in optical communication with the second lens; an aperture stop in optical communication with the third lens; and a fifth lens in optical communication with the fourth lens.
 60. The lens assembly of claim 59, wherein the first lens is a meniscus lens.
 61. The lens assembly of claim 59, wherein second lens is a meniscus lens.
 62. The lens assembly of claim 59, wherein the third lens is a meniscus lens.
 63. The lens assembly of claim 59, wherein the fourth lens is a meniscus lens.
 64. The lens assembly of claim 59, wherein the fifth lens is a bi-convex lens.
 65. The lens assembly of claim 59, wherein the first lens is a piano-convex lens.
 66. The lens assembly of claim 59, wherein the fourth lens is a bi-concave lens.
 67. A lens system comprising a plurality of lens elements, and an aperture stop, each lens element having a lens surface defined by a radius of curvature (r), a thickness (d), an index of refraction (n), and a dispersion (v), the plurality of lens elements being spaced from each other by a distance (d), the lens system satisfying at least one of the following conditions: a) 0.98*f<d₁+d₂+d₃+d₄+d₅+d₆+d₇+d₈+d₉+d₁₀+d₁₁+d₁₂+d₁₃+d₁₄<1.02*f; or b) 0.47*f<d₁+d₂+d₃+d₄+d₅+d₆+d₇+d₈+d₉<0.61*f; or c) 20.4 mm<f₁<30.5 mm when assembly scaled to f=25 mm; or d) −100 mm<f_(2,3)<15 mm when assembly scaled to f=25 mm; or e) 1.49<n₁<1.52 and v₁≧70; or f) 1.8<n₂ and 24<v₂<26; or g) −50 mm<f₄<−35 mm when 1.5<n₄<1.72 and when assembly scaled to f=25 mm; or h) 110 mm<f₅<540 mm when n₅>1.7 and when assembly scaled to f=25 mm; or i) r₇/r₁₀<0.3 when n₄/n₅>0.98; or j) r₇/r₁₀>0.5 when n₄/n₅<0.90; where: f represents an effective focal length of the plurality of lenses; f₁ represents a focal length of a first lens element; f₄ represents a focal length of a fourth lens element; f₅ represents a focal length of a fifth lens element; f_(2,3) represents a focal length of a combination of a second lens element and a third lens element; d₁ represents a thickness of the first lens element; d₂ represents a gap distance from an image side surface of the first lens element to an object side surface of the second lens element; d₃ represents a thickness of the second lens element; d₄ represents a thickness of the third lens element; d₅ represents a gap distance from an image side surface of the third lens element to the aperture stop; d₆ represents a gap distance from the aperture stop to an object side surface of the fourth lens element; d₇ represents a thickness of the fourth lens element; d₈ represents a gap distance from an image side surface of the fourth lens element to an object side surface of the fifth lens element; d₉ represents a thickness of the fifth lens element; d₁₀+d₁₁+d₁₂+d₁₃+d₁₄ represents a gap distance from an image side surface of the fifth lens element to an image plane; n₁ represents an index of refraction of the first lens element; n₂ represents an index of refraction of the second lens element; n₄ represents an index of refraction of the fourth lens element; n₅ represents an index of refraction of the fifth lens element; v₁ represents a dispersion of the first lens element; v₂ represents a dispersion of the second lens element; v₄ represents a dispersion of the fourth lens element; v₅ represents a dispersion of the fifth lens element; r₇ represents a radius of curvature of the object side surface of the fourth lens element; and r₁₀ represents a radius of curvature of the image side surface of the fifth lens element.
 68. The lens system according to claim 67, the lens system satisfying each of the conditions.
 69. The lens system according to claim 67, the lens system satisfying a plurality of the conditions.
 70. The lens system according to claim 67, the lens system further comprising a first planar plate, wherein d₁₁ represents a thickness of the first planar plate, and wherein d10 represents a gap distance from the image side surface of the fifth lens element to an object side surface of the first planar plate.
 71. The lens assembly according to claim 70, wherein the first planar plate is a filter plate.
 72. The lens system according to claim 70, the lens system further comprising a second planar plate, wherein d12 represents a gap distance from an image side surface of the first planar plate to an object side surface of the second planar plate, wherein d₁₃ represents a thickness of the second planar plate, and wherein d₁₄ represents a gap distance from an image side surface of the second planar plate to the image plane
 73. The lens system according to claim 72, wherein the second planar plate is a cover glass. 